1. I would NOT be pressing head to start with. It is aluminum. Not stainless steel, it does not like being bent and rebent. Of course, your friend should have better knowledge on that. Simple mating surface re surfacing should suffice. That, pretty much, answers your question - why would you be messing with camshafts? A head that warped so much that it influenced cam jourlnals should be tossed, not repaired. Besides, you can easily review cam bearings condition after head removal. Valve stem seals - definitely replaced.
2. Toyota re designed pistons due to excessive oil consumption on hybrid engines. Allegedly, that was the case for hybrid engines only, as their pistons are different. If your engine was tight and did not use oil, then don't worry about pistons. Now, new rings will definitely not hurt. If your engine did burn oil, you want to talk to dealer if there were updated pistons for your particular engine. They have larger oil channels and rings are different. Again, if that was not an issue, don't mess with it.
Hone and ring compressor/removal tools are ready rentable from any parts store. Just don't score pistons when removing rings.
Heck, you could simply pull pistons out and soak them, with rings on, in kerosine overnight, to remove any crud and for rings to spring back.
Cylinder condition will have ot be assessed after head removal. I'd have replaced chain tensioner same time. Tensioner and guides. My mech would have replaced water pump also. He's very adamant about replacing as much as possible "while you there". Crap tends to happen after a job was done. So why not to do it all anyway.
Now, all this is going to cost you. Head machining, parts. It may be more cost efficient to actually get a used engine. As, when overheated, seals tend to go bad and start leaking. Certified used engine from Japan would have been ideal but you know, how much fraud goes there.
Ultimately, it is your decision, how to proceed.